Are you ready to go on a carbon diet?

According to the Carbon Trust, a private company backed by the British government to accelerate development of climate-change technologies, 80 percent of a product's emissions arise further back in the supply chain – before consumer usage.

As British consumers grapple with the new labels, retailers in the United States are taking a limited approach.

Most companies don't understand their full environmental impacts, he says.

Those making efforts to examine their carbon footprints often do so without transparency – essential to generating both customer support and supply-chain innovation.

At Wal-Mart, consumer transparency is largely tied in to its corporate press releases, a growing assortment of eco-labeled products, and in-store awareness campaigns. A more robust effort is the company's "Love, Earth" jewelry, which enables customers to use the Internet to map where the jewelry's gold and silver were mined and manufactured, including information on how the mines manage cyanide and waste dumps.